The Function Of Differential Proteins In Salivary Glands On Virus Transmission By Viruliferous Laodelphax Striatellus

Laodelphax striatellus(Homoptera:Delphacidae)is an important agricultural pest,not only infesting cereal plants,but also as a vector of several viruses.The Rice stripe virus(RSV),a typical member of Tenuivirus,is transmitted by the L.striatellus in a persistent-propagative manner and has caused serious yield losses in rice production in East Asia.During the general transmission process of persistent-propagative viruses,virions first accumulate in the midgut lumen of the insect and then pass through the midgut wall to disperse into the hemolymph or nervous tissues,then into the salivary glands from where the viruses can be introduced back into the host plant during insect feeding.It is obvious that the salivary gland is the last barrier that RSV must overcome.Our previous study indicated that the expressions of some proteins,such as ATP synthase subunit alpha(LsATP),mitochondrial import inner membrane translocase(LsMIT),NADP-dependent malic enzyme(LsNADP),tubulin alpha-2(LsTUB),ubiquitin-60S ribosomal protein L40 precursor(LsUBI)and voltage-dependent anion-selective channel(LsVDAC)in the salivary glands of viruliferous L.striatellus were significantly higher than those of naive vectors.Moreover,the mRNA expression levels of the above six proteins were significantly higher in in the salivary glands or whole body of viruliferous L.striatellus,compared with the naive vectors.RNAi silencing of LsATP,LsMIT and LsTUB were used to examine their effects on RSV transmission in viruliferous L.striatellus.In this study,we used RNAi silencing to study the effect of the other three genes,LsUBI,LsNADP and LsVDAC on the RSV transmission rate of viruliferous L.striatellus.To explore function of the genes that can change RSV transmission rate,we examined the effect of functional genes on the relative expression level of RSV in different tissues or organs in viruliferous L.striatellus.The results were as follows.(1)RNAi silencing of LsUBI,LsNADP and LsVDAC genes were used to examine their functions in RSV transmission by viruliferous L.striatellus.The significance of RNA interference was obtained.The dsRNA decreased relative expression level of target gene by 75.8%for LsUBI,77.8%for LsNADP,and 77.4%for LsVDAC,respectively,compared to controls.No obvious difference was observed in virus transmission rate by viruliferous L.striatellus treated with LsNADP or LsVDAC compared to control,indicating that LsNADP and LsVDAC had less significance in RSV transmission.Virus inoculation rate of viruliferous L.striatellus treated with dsLsUBI was 4.0%,and was 12.I%of the control.It indicated that LsUBI played an important role in RSV transmission.(2)To investigate the mechanism of the changed RSV transmission rates caused by LsTUB and LsUBI,we examined the effect of LsTUB and LsUBI on the relative expression level of RSV in different tissues or organs in viruliferous L.striatellus.LsTUB and LsUBI can be detected in the salivary glands,the midgut lumen,ovary and hemolymph of viruliferous L.striatellus.The relative expression level of RSV in the salivary glands,the midgut lumen,ovary and hemolymph of viruliferous L.striatellus treated with dsLsTUB were decreased by 15.4%,35.1%,24.3%and 31.0%,respectively,compared with the untreated control.RNA interference of LsUBI decreased the relative expression level of RSV in the salivary glands by 30.3%,but did not affect the relative expression level of RSV in the midgut lumen,ovary or hemolymph.The results indicated that LsTUB may play important roles while RSV pass through the midgut wall or overcome the salivary glands,and LsUBI may help RSV overcome the salivary glands in viruliferous L.striatellus.